African Union and Somali officials say their troops have made “strong progress” in a fast-moving offensive to capture a key al-Shabab rebel stronghold northwest of the capital, Mogadishu.

A statement issued Wednesday said troops were advancing to the area of Elasha in the strategic Afgoye corridor between Mogadishu and the regional capital, Baidoa, and that a senior al-Shabab commander was killed in heavy fighting.

In an interview with VOA, Somali Defense Minister Hussein Arab Essa said the first stage of the AMISON offensive was almost complete and predicted troops would seized Afgoye within two days. He said the two-fold objective of the operation is to secure the Mogadishu-Afgoye road and ensure the safety of civilians.

The heaviest fighting was reported in an area that is home to the largest community of internally displaced people in the world. An estimated 400,000 refugees, forced from their homes by famine and war, are said to be living in squalid camps.

Al-Shabab has held the Afgoye corridor for years in its campaign to overthrow Somalia's United Nations-backed transitional government and impose strict Islamic law. The group once controlled most of southern and central Somalia, but has steadily lost ground in the past 18 months to AU, Somali, Kenyan and Ethiopian forces.

The U.N. mission in Somalia has described the offensive as a “carefully planned operation” in which troops are taking every precaution to prevent harm to civilians.

The U.N. Humanitarian Coordinator for Somalia, Mark Bowden, on Wednesday reiterated his call for all parties to make efforts to minimize the impact of conflict on civilians, saying that further fighting could lead to displacement and straining of temporary settlements.

AU and government officials said al-Shabab has been preventing aid agencies from operating in the area.